In order to enhance the gray scale of an image, the gray scale is corrected by calculating, with respect to plural image signals corresponding to respective pixels constituting the image, a maximum and a minimum of gray levels for each color component, and setting the maximum and minimum calculated for each color component as the maximum and minimum of the dynamic range of the gray scale for each color component in the image signal system of the corrected image (see, for example, Patent Documents 1 and 2).